Carbon is a chemically stable substance. Numerous types of carbon catalysts (activated carbon) are produced by various methods of manufacture and various methods of activation. For example, a method which comprises impregnating peat or wood chips with an aqueous metal chloride solution and then carbonizing the resultant impregnation product at elevated temperatures, a method which comprises causing the surface of carbon or graphite to be reacted upon by steam, air, or carbon dioxide gas at elevated temperatures thereby effecting oxidizing etching of the surface, a method which comprises immersing carbon in a hot bath of concentrated phosphoric acid, and a method which comprises impregnating carbon with sodium hydroxide or a thiocyanate and subsequently subjecting the impregnated carbon to a thermal treatment thereby etching the surface of carbon have been known to the art.
These methods which involve surface etching of carbon, however, have the following common drawbacks.
(I) Since hot or corrosive chemical substances are used for etching, these methods can not be applied to composite carbon materials prepared by incorporation of substances deficient in resistance to heat and corrosion (high molecular substances).
(II) Chemical substances used for etching tend to remain in the produced carbon catalysts and give rise to impurities.
(III) Disposal of the chemical substances used in etching tends to cause environmental pollution.
(IV) The etching processes involved are not easy to control and manage.
For the solution of these problems, the conventional wet etching method has been switched to the dry etching method in the process for manufacture of semiconductors, for example. This fact suggests that establishment of a suitable dry etching method, therefore, will suffice for the solution.